Powder formed from mineral or rock material with controlled particle size distribution for thermal films

ABSTRACT

An ultra-fine powder formed from a naturally occurring mineral or rock material and having a controlled or “engineered” particle size distribution (PSD) to match the infrared spectra with a maximum particle size in the range of 14-17 microns measured as either D99, or preferably D95, and a minimum particle size D5 in the range of 4-7 microns. Preferably the maximum particle size is about 15 microns, the minimum particle size is about 5 microns and the D50 particle size is about 8-10 microns with the moisture content of the particle size “engineered” powder being less than about 0.20 percent by weight and preferably about 0.05 to 0.08 percent by weight of the powder. This specially “engineered” ultra-fine powder is used to reduce the thermicity of thermal film to a value less than about 20%.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of patent application Ser. No.13/420,757 filed on Mar. 15, 2012 (now U.S. Pat. No. 8,795,427), whichis a continuation of patent application Ser. No. 12/237,628 filed onSep. 25, 2008 (now U.S. Pat. No. 8,182,601) which claims priority uponU.S. provisional application Ser. No. 61/124,498 filed Apr. 17, 2008,all of which are incorporated by reference herein.

The present invention relates to the art of fine grain nepheline syenitepowder as a category in the nepheline syenite industry and moreparticularly to a novel ultra-fine nepheline syenite powder havingcontrolled particle size especially designed for thermal films. Thermalfilms using the novel ultra-fine nepheline syenite powder constitutes afurther aspect of this invention.

Although the preferred implementation of the present invention is anepheline syenite powder, the invention can also be used to engineer theparticle size distribution (PSD) of other minerals or rock materials foruse in thermal films. Such powder with the novel selected PSD may alsobe used for other applications of films or coatings. Irrespective ofthis broad definition of the engineered PSD of mined natural occurringmaterials, the description shall concentrate on the preferred embodimentusing nepheline syenite, which is a rock composition or material.

Background of Nepheline Syenite Powder

Unimin Corporation of New Canaan, Conn. is a leading source of mined rawnepheline syenite, which is a natural occurring rock formed from severalminerals and is found in deposits in only limited areas of the world.The nepheline syenite industry has developed technology that is used forgrinding and crushing raw nepheline syenite rock and then converting theparticulated nepheline syenite into usable fine grain powder. Thus, thefield to which the present invention is directed is the industry ofnepheline syenite and the technology of converting nepheline syenite asmined into usable form that is a commercial powder. In about 2001,Unimin Corporation, after substantial research and development, inventedan ultra-fine nepheline syenite powder, which powder was believed to bethe smallest commercially available and economically produciblenepheline syenite powder. This ultra-fine powder had a maximum particleor grain size D99 substantially above 20 microns. However, it wasclassified as “ultra-fine” nepheline syenite powder because it had amaximum particle size of less than about 20 microns. Such “ultra-fine”nepheline syenite powder had the smallest commercially available grainsize. At about this time, Unimin Corporation invented a nephelinesyenite powder that had a maximum particle size of about 20 microns anda minimum particle size of less than 1-2 microns, which was caused by aremoval of very small particles or fines. This powder was developed asan anti-blocking agent and was sold under the trademark MINBLOC HC1400.The particle size distribution of MINBLOC HC1400 was over 15 micronsbetween the D95 and D5 particle sizes, as shown in FIGS. 14 and 15. Suchanti-blocking agent and other nepheline syenite powders designated as“ultra-fine” and having only a controlled maximum particle size were theprior art nepheline syenite powder closest to the ultra-fine powder ofthe present invention.

Thermal Film Using the Invention

The novel nepheline syenite powder of the present invention hasproperties developed to make it a superior filler for thermal films.Such films are used in a light transmitting canopy for a chamber orgreenhouse for growing vegetation, such as plants and trees. Agreenhouse has a canopy including a thermal film. Light radiation passesthrough the greenhouse canopy including a thermal film, so the lightwarms the interior of the greenhouse and facilitates absorption of sunrays by the plant life. The solar radiation passes through the canopy,including a thermal film, to the extent that the film has transparency.The amount of light and heat is determined by the transmittance of thefilm. At night, the temperature within the greenhouse drops according tothe amount of energy transmitted back through the thermal film. Asubstantial drop in the temperature can cause the plants to suffercertain physiological damage. Thus, a thermal film is used in the canopyfor the purpose of allowing energy from the sun to be transmitted intothe greenhouse in the day time and then a reduced amount of heat energyto leave the greenhouse at night time, i.e. when the sun is not heatingthe greenhouse.

During day time, electromagnetic radiation from the sun passes throughthe thermal film. The constituents of solar energy are visible lightand, to a lesser extent ultraviolet and near-infrared radiation. Duringthe night time, the inside of the greenhouse radiates heat in the rangeof mid-infrared. This radiation is black-body radiation and happens topeak around 7 to 14 microns for objects that are at room temperature orslightly colder. It is this 7-14 microns mid-infrared radiation that thepresent invention traps to avoid heat loss of the greenhouse. Theinvention saves energy during periods that the temperature outside thegreenhouse is lower than inside the greenhouse, especially during nighttime. Consequently, it has been found that nepheline syenite powder isvery beneficial in use as filler for such thermal film. It isinexpensive and has a high visible light transmittance. The presentinvention utilizes the known advantages of nepheline syenite powder,while drastically reducing the amount of heat energy radiated backthrough the covering film. This loss of heat energy is measured as thethermicity of the film. Using the FTIR it is possible to measure thefraction (%) of infrared light in the range of 7-14 microns that passesthrough the film, which is called “thermicity.” Consequently, the heatloss upwardly through the thermal film is defined as the “thermicity”which defines the amount of heat energy maintained in the greenhouse attimes when the loss of heat by infrared radiation is reversed in thegreenhouse. “Heat loss” in this description is the loss due toelectromagnetic radiation and not due to other mechanisms, such asconductive heat transfer, which is insignificant.

The present invention is directed to an ultra-fine powder whichmaintains the advantages of nepheline syenite powder including its lowcost and its free silica characteristic, which novel ultra-fine powderhas a “tailored” particle size profile that allows the film to maintainhigh transmittance or transparency and with a dramatic reduction inthermicity. Nepheline syenite has the benefit of resulting in a thermalfilm that has high transparency or visible light transmission. Itappears that this characteristic is due to the good match in refractiveindex between the film and nepheline syenite. This is a property ofnepheline syenite. The particle size does not affect transparency.However, the particle size does affect thermicity. Thus, the inventionuses this discovery. Of course, nepheline syenite also has thecommercial advantage of not having any free silica. The invention is anultra-fine powder, preferably nepheline syenite powder, with a“tailored” particle size profile where the particle size isapproximately in the range of the wave length of the infrared radiationthat is to be scattered back into the greenhouse. This concept is basedupon Mie theory which suggests that particles scatter electromagneticradiation (light) when they are of the same size as the radiation.

DEFINITIONS

Nepheline syenite is a rock in powder form constitutes a fine grainsilica deficient silicate in the form of a sodium potassium aluminosilicate. The maximum grain size as used herein is a target valuedefined as D99 or D95 and the minimum grain size as used herein is thetarget value defined as D5. The actual maximum particle size of thepowder is really defined as size D99 and the minimum is the size D1. Theterms “maximum” and “minimum” grain or particle sizes relate to targetedlevels unless otherwise indicated. This is common usage in the smallpowder industry. The loading of nepheline syenite powder in a coating orfilm is defined as the percentage by weight of the filler in thereceiving matrix. Substantially moisture free means less than 1.0% byweight of moisture and preferably less than about 0.8% by weight.

STATEMENT OF INVENTION

The present invention relates to a filler for thermal films, whichfiller has controlled minimum particle size D5 and is an “ultra-fine”nepheline syenite powder with a controlled maximum particle size D95.Control of the maximum size particles in the nepheline syenite powder isused to substantially reduce the abrasive properties of the filler whenit is processed in the coating or film. Accurate control of the minimumsize particles is used to reduce the gloss, improve clarity and reduceyellowing of the films. The nepheline syenite powder of the presentinvention shows low gloss or a matte finish and less abrasion toprocessing or application equipment. These properties are the result ofusing the novel ultra-fine nepheline syenite powder of the presentinvention. When used in a thermal film, the novel powder of the presentinvention has the primary objective of reducing thermicity whileallowing excellent transparency.

The novel nepheline syenite powder of the present invention has anarrowed size between the maximum controlled grain size D95 and theminimum controlled grain size D5. This range is 10-12 microns.Consequently, the grain size distribution of the ultra-fine nephelinesyenite powder of the present invention, impart very specificcharacteristics to the thermal film because of the narrow particle sizedistribution, and matching of the particle size to a selected part ofthe mid-range wave length of infrared light. Indeed, the new ultra-finenepheline syenite powder of the present invention has a controlledmaximum grain size D95 of about 15 microns and a controlled minimumgrain size D5 of about 4-7 microns. This is substantially greatercontrolled size over any prior art. The grain size distribution betweenthe controlled maximum grain size and the controlled minimum grain sizeis generally less than about 12 microns. This narrow range of grain sizedistribution imparts a specific and uniform physical property to thethermal film using as a filler the novel ultra-fine nepheline syenitepowder of the present invention.

In accordance with an aspect of the present invention not only does theultra-fine nepheline syenite powder include a controlled minimum grainsize, but also includes an accurately controlled maximum grain size. Bycontrolling both the upper and lower grain sizes of the “ultra-fine”nepheline syenite powder, the aforementioned narrow controlled range ofparticle size distribution is obtained. Another aspect of the inventionis the fact that the novel nepheline syenite powder with a controlledminimum grain size of 4-7 microns and/or a controlled maximum grain sizeof less than 20 microns is manufactured by a feedstock which is apre-processed nepheline syenite powder, having a maximum grain size ofless than about 150 microns and, indeed, in the range of 20-150 microns.Thus, the present invention involved the processing of a previouslyprocessed nepheline syenite powder to have a preferred maximum grainsize of 20-150 microns, but preferably about 100 microns.

In accordance with the present invention, there is provided a newultra-fine nepheline syenite powder produced from a pre-processednepheline syenite powder feedstock having a maximum grain size D99 ofless than about 150 microns. The novel ultra-fine nepheline syenitepowder of the present invention has a moisture content of less than 1.0%by weight and preferably less than 0.8% by weight. In accordance withthe invention, this particle size distribution range D5 to D95 is lessthan about 10-12 microns. Consequently, the distribution of particles isin a very narrow range to give consistent and well defined physicalcharacteristics to films using this new ultra-fine nepheline syenitepowder.

In accordance with another aspect of the present invention, the novelultra-fine nepheline syenite powder of the present invention is producedfrom the feedstock comprising a pre-processed nepheline syenite powder,which feedstock is processed by an air classifier. Indeed, the novelultra-fine nepheline syenite powder is formed by various processes, oneinvolving air classification, the other a series of air classifiers andthe other a mill and air classifier in series constituting a continuousprocess. In accordance with an aspect of the present invention, the millused in one method for producing the novel ultra-fine nepheline syenitepowder is an air jet mill of the type using opposed air jets. When aseries of air classifiers are used in the method for producing the novelultra-fine nepheline syenite powder, one air classifier stage removesthe upper grain size and another air classifier stage removes the lowergrain size to produce the nepheline syenite powder having a very narrowparticle range between a controlled maximum value and a controlledminimum value.

The novel ultra-fine nepheline syenite powder is produced in acontinuous process whereby pre-processed nepheline syenite powderfeedstock is passed through a series of air classifier stages or a batchmethod wherein the nepheline syenite powder feedstock is ground in anopposed jet mill and then classified internally and externally. Thepre-processed nepheline syenite powder can be powder of the type havinga maximum particle size of less than about 100 microns.

In accordance with a further major aspect of the present invention,there is provided a thermal film including ultra-fine nepheline syenitepowder with a controlled maximum grain size D95 of about 15 microns anda controlled minimum grain size D5 in the range of about 4-7 microns andpreferably about 5 microns. The ultra-fine nepheline syenite powderfiller in the thermal film constituting this aspect of the presentinvention is added to the film with a loading factor of 5-25% by weightof the coating or film.

Nepheline syenite is naturally occurring rock constituting a mixture ofNa feldspar, K feldspar and nepheline. (NaAlSiO4). It has a low level offree silicon dioxide. This material can be described as either syeniticor syenitic feldspar. Consequently, the present invention is applicableto nepheline syenite and also to other syenitic materials havingdrastically low free silicon dioxide. This general description ofnepheline syenite is applicable to an understanding of the presentinvention and is used to define the nepheline syenite rock formationconstituting the preferred material used in practicing the invention.This invention comprises a unique “ultra-fine” powder, use of suchpowder as a filler for thermal films and thermal films using this novelpowder. The preferred material for making the powder is nephelinesyenite and specifically commercial nepheline syenite powder with amaximum particle size in the range of 20-150 microns.

A primary aspect of the present invention is the provision of anultra-fine powder substantially free of silica and formed from anaturally occurring mined substance with a controlled maximum grain sizeD95 of about 15 microns, a controlled minimum grain size D5 of about 4-7microns and a D50 grain size in the general range of about 8-10 microns.This novel powder has a moisture content of less than 1.0% by weight andthe maximum mode of the PSD curve for the novel powder is between 7-14microns. As a feature of the invention, the particle size distributionbetween D95 and D5 is in the range of 10-12 microns. Thus, the powdershave a controlled very narrow particle size distribution. The PSD curveis quite narrow. By profiling the particle size, the thermal filmsprepared with the ultra-fine powder as defined in the invention have animproved thermicity as measured in the range of 7-14 microns where thereis maximum heat loss by radiation. This novel powder is “ultra-fine” tosubstantially increase transmittance of a film using the powder as afiller thereby allowing a high amount of incoming heat energy throughthe film. But a low thermicity imparted by the novel powder prevents ahigh amount of heat energy to be dissipated outwardly through thethermal film. As is well known, incoming heat from the sun is in thenear-infrared range and the heat leaked from inside the greenhouse is inthe mid-infrared range.

In accordance with the practical implementation of the invention, thepowder having the particle profile that creates the above definedphysical characteristics is an ultra-fine nepheline syenite powder.Thus, the advantages of nepheline syenite, including its low cost andhigh transmittance is obtained in the novel powder. Both the“ultra-fine” characteristics of the powder and the fact that the powderis nepheline syenite provides substantial advance in the filler forthermal films. The tailored particle size profile adds to theseadvantages by reducing thermicity and reducing the particle rangebetween the controlled maximum particle size and the “controlled”minimum particle size. This narrow particle size span or range givesimproved control over the properties of the film.

In accordance with another aspect of the present invention, there isprovided a thermal film having fillers constituting the novel ultra-finepowder as defined above. In accordance with this aspect of theinvention, the thermal film is selected from the class consisting ofpolyethylene and ethylene vinyl acetate. The loading of the filler is atleast 5% by weight of the film. In accordance with an aspect of theinvention loading at least 5% and preferably is in the general range of5-25% by weight of the film.

In accordance with another aspect of the invention, there is provided anultra-fine nepheline syenite powder produced from a feedstockconstituting pre-processed nepheline syenite powder with a maximum grainsize D99 in the range of 20-100 microns. This feedstock is pre-processedand may or may not be merely a commercially available nepheline syenitepowder. The ultra-fine nepheline syenite powder produced from thefeedstock has a moisture content of less than 1.0% by weight, acontrolled minimum particle size or grain size D5 in the range of 4-7microns and a controlled maximum grain size or particle size D95 ofabout 15 microns. The mean grain size or particle size D50 is in therange of 8-10 microns and the maximum node of the PSD curve for thepowder is in the range of 7-14 microns.

Another aspect of the present invention is provision of an ultra-finenepheline syenite powder, as defined above, wherein the startingfeedstock is a commercial nepheline syenite powder; such as a commercialMinbloc powder. A pre-processed nepheline syenite powder is convertedinto a particle size distribution profile which involves removal ofparticles above a given grain size D95 of about 15 and below a grainsize D5 of a selected amount, which selected amount is preferably 5microns, but is in the range of 4-7 microns. In practice, the groundnepheline syenite feedstock has a medium particle size D50 of 15 micronsand a maximum particle size D99 of 100 microns. The selected feedstockgenerally has a large fraction of particles in the 7 to 14 micron range.In accordance with an aspect of the invention the pre-processedfeedstock has a D99 particle size greater than 20 microns and less thanabout 100-150 microns.

In accordance with a broad aspect of the present invention, there isprovided a novel ultra-fine powder formed from a naturally occurringmineral or rock material with a refractive index (RI) of about 1.4-1.6.This refractive index is selected to produce a film generallytransparent to visible light. Preferably, the refractive index is in therange of 1.46-1.57. The mineral or rock material having such values forthe refractive index when the powder is in film has been found to bematerial selected from the class comprising silica (including groundnatural and diatomaceous) cristobalite, feldspar, quartz, nephelinesyenite, kaolin, alumina trihydrate, talc, attapulgite, pyrophyllite,calcium hydroxide, magnesium hydroxide and hydrotalcite, but preferablythe class consisting of silica (including ground natural anddiatomaceous), cristobalite, feldspar, quartz, nepheline syenite,kaolin, talc, attapulgite and pyrophyllite. This preferredclassification has been processed as disclosed. By definition,“ultra-fine” powder is powder having a maximum particle size of lessthan about 20 microns wherein the maximum grain size is the D99 grainsize. In accordance with this broad aspect of the invention, theultra-fine powder has a particle size distribution tailored tocorrespond with the wave length of infrared light and is generallytransparent to visible light.

In accordance with another broad aspect of the present invention, thereis provided a novel ultra-fine powder formed from a mineral or rockmaterial with a Mohs hardness of at least 5. As stated before,“ultra-fine” powder is powder having a maximum particle size of lessthan about 20 microns wherein the maximum grain size is the D99 particlesize. In accordance with this aspect of the invention, the novelultra-fine powder has a particle size distribution tailored or“engineered” to correspond with the specific PSD as defined in thisdisclosure. Whether the powder is defined by the Mohs number or by itsrefractive index, the ultra-fine powder of the present invention has acontrolled particle size distribution with a maximum particle size D99,or preferably D95, in the range of 14-17 microns and a minimum particlesize D5 in the range of 4-7 microns. It has been found that thepreferred material is syenitic, such as nepheline syenite. However, whenthe material is selected based upon Mohs number, the mineral or rockmaterial that is used as feedstock to form the novel ultra-fine powderis selected from the class comprising nepheline syenite, feldspar,silica, quartz, cristobalite and tridymite.

The use of any of these naturally occurring, mined materials having thePSD of the present invention reduces the thermicity of a thermal film,in which such powder is used as a filler. Indeed, the invention is thenovel particle size engineered ultra-fine powder having a specific PSD.

In accordance with the preferred definition of the present invention,the maximum particle size D95 is about 14-17 microns and the minimumparticle size D5 is about 5 microns. Furthermore, the D50 particle sizeis in the range of about 8-10 microns. In another aspect of this broadaspect of the invention, the ultra-fine powder has a moisture contentthat is less than about 0.20% by weight and preferably less than about0.1% by weight. Indeed, in the preferred implementation the moisturecontent is less than about 0.08% by weight of the powder. These conceptsconstitute one of the broadest aspects of the present invention, whichinvention involves the use of a mined, naturally occurring mineral orrock material, which naturally occurring material is processed to havean engineered particle size distribution, which PSD is quite narrow andmatches the wavelength of the infrared light spectra.

In accordance with an alternative implementation of the invention, thenaturally occurring mineral or rock material used to produce the novelultra-fine powder with the selected PSD, is a hard material having aMohs number of at least 5. This mineral or rock material is used topractice the invention and is selected from the class of hard materialscomprising nepheline syenite, feldspar, silica, quartz, cristobalite andtridymite.

In accordance with the preferred implementation of the presentinvention, the naturally occurring material, from which the ultra-finepowder is formed, has little or no free silica; however, in a broaderaspect of the invention, this beneficial feature of substantially nofree silica is merely a further definition of a preferred implementationof the present invention.

In accordance with another aspect of the present invention, there isprovided a method of processing naturally occurring mineral or rock tobe used primarily for thermal film. The preferred method of making thenovel powder is a method comprising providing ground feedstock formedfrom a naturally occurring mineral or rock material having a refractiveindex of about 1.4-1.6, grinding the feedstock in an opposed jet mill,classifying the ground feedstock in the mill with a classifier to passan intermediate powder from the mill. The intermediate powder has amaximum particle size of about 14-17 microns. Then, the intermediatepowder is passed through an air classifier to remove particles having aparticle size of less than 4-7 microns. This is the preferred method ofproducing the ultra-fine powder used for thermal film.

In accordance with another aspect of the present invention, there isprovided an alternative method of producing the ultra-fine powder to beused in thermal film. This method involves providing a feedstock formedfrom a naturally occurring mineral or rock having a refractive index ofabout 1.4-1.6. The feedstock is then ground and an intermediate powderis produced by passing the ground feedstock through a first airclassifier to remove particles having a first size greater than a valuein the range of 14-17 microns. Thereafter, the intermediate powder ispassed through a second air classifier to remove particles having asecond size less than a value in the range of 4-7 microns. This methodis an alternative method developed for producing ultra-fine powder foruse in making thermal film. The starting material for this method hasbeen found to be a material selected from the class comprising silica(including ground natural and diatomaceous), cristobalite, feldspar,quartz, nepheline syenite, kaolin, talc, attapulgite and pyrophyllite.

The primary object of the present invention is the provision of anultra-fine powder having a tailored particle size profile created toimprove properties of thermal films. The tailored profile involves acontrolled maximum particle size, a controlled minimum particle size andwith the range of these particles sizes being between about 4 micronsand about 15 microns. In this manner, the particle size distributionmatches a selected range of the infrared radiation spectra, which rangecontrols the thermicity of a film using the ultra-fine powder. Thepowder is preferably nepheline syenite and is produced frompre-processed nepheline syenite powder. However, the powder can be of asyenite material, which means a material that is composed of the Na andK feldspar with little or no silica.

Another object of the present invention is the provision of anultra-fine powder formed from a mineral or rock material with a Mohshardness of at least 5, wherein the powder has a controlled or“engineered” particle size distribution (PSD) with a maximum particlesize, preferably D95 in the range of 14-17 microns and a minimumparticle size D5 in the range of 4-7 microns. In this manner, a majorityof the engineered powder matches a selected range of the infraredradiation spectra, which range controls the thermicity of the film usingthe ultra-fine powder as a filler. The powder is formed from a minedmaterial having the aforementioned engineered particle sizedistribution, which PSD is narrow and matches properties of infraredlight. However, a further object is the use of this ultra-fine powder invarious films and coatings to reduce thermicity or to obtain otherspecific properties, such as hardness. The preferred starting materialfor this object is material selected from the class comprising nephelinesyenite, feldspar, silica, quartz, cristobalite and tridymite.

Yet another object of the present invention is the provision of anultra-fine powder formed from a mineral or rock material having arefractive index in the range of 1.4-1.6 and preferably in the range of1.46-1.57. This material forms the feedstock to produce powder havingthe controlled or “engineered” particle sizes defined in thisapplication which particle sizes have a maximum value of either D99 orD95 in the general range of 14-17 microns and a minimum particle size D5in the general range of 4-7 microns. Preferably, irrespective of thedefinition of the feedstock used in making the ultra-fine powder, themaximum particle size is about 15 microns and the minimum particle sizeis about 5 microns. The selection of the feedstock by either a Mohsnumber of at least 5 or by a refractive index in the general range of1.4-1.6 does not change the ultimate characteristics of the novelpowder, which ultimate characteristics include an engineered maximumgrain size in the range of 14-17 microns and a minimum grain size in thegeneral range of 4-7 microns. To provide an ultra-fine powder where therefractive index is a part of the invention, the starting material isselected from the class comprising silica (including ground natural anddiatomaceous), cristobalite, feldspar, quartz, nepheline syenite,kaolin, alumina triydrate, talc, attapulgite, pyrophyllite, calciumhydroxide, magnesium hydroxide and hydrotalcite. The preferred startingmaterial for this object is material selected from the class comprisingsilica (including ground natural and diatomaceous), cristobalite,feldspar, quartz, nepheline syenite, kaolin, talc, attapulgite andpyrophyllite. These materials have been processed as herein disclosed.

In accordance with even yet another object of the invention, thetailored particle size profile has a “controlled” D95 size, a“controlled” D5 size and a specific D50 size to provide a powder havinga narrow spread between the D5 and D95 particle sizes.

In accordance with the invention, there is provided a thermal film usingthe novel filler powder having a tailored particle size profile andother features mentioned above.

Another object of the present invention is the provision of anultra-fine nepheline syenite powder that allows for more visible lightto pass through a thermal film using the powder as a filler. The fineparticle size profile and the fact that nepheline syenite powder isused, instead of another mineral powder, contributes to an increasedtransmittance. Thus, more visible light, and in particular photosynthetically active radiation (PAR), passes through the thermal film topromote photosynthesis. The thermal film using the ultra-fine nephelinesyenite powder of the present invention can be loaded higher withoutsacrificing too much incoming solar energy. With high loading, thethermal film can be made less expensive since the resin costs more thanthe filler. The thermicity of the highly filled thermal film issubstantially lower than for films with other fillers. Indeed, the morethermal filler used, the better the thermicity. Consequently, the firstbenefit of the new powder is less heat loss. A secondary benefit is thatthe film can be made cheaper. In summary, by using nepheline syenitepowder with a tailored particle size parameters of the presentinvention, the thermal film may be loaded to a high amount in thegeneral range of 20-25% by weight while still maintaining a hightransmittance and a low thermicity. As indicated the loading is at least5% by weight of the film. The low thermicity characteristic is obtainedby selecting the controlled maximum grain size and the controlledminimum grain size to match a particular wave length range of infraredlight that transmits heat energy in the reverse direction through thefilm using the novel powder as a filler. The particle size of the newpowder is “controlled” to approximately the range of the infraredradiation to be scattered back into the greenhouse. This propertyutilizes the Mie theory mentioned before.

Representative Particle Systems

It is instructive to explain certain designations and nomenclaturedescribed herein. Particle sizes, unless indicated otherwise, are givenin microns, 10⁻⁶ meters. As will be appreciated by those skilled in theart, particle sizes are expressed in diameters. Although diameters implya spherical or round shape, the term diameter as used herein also refersto the span or maximum width of a particle that is not spherical.Typically, ranges of particle sizes or size distributions are noted. Forexample, for a range of 5 to 15 microns, a designation of “5×15” istypically used. Another designation used herein is “D_(n)” where n issome numerical value between 0 and 100. This value refers to aproportion or percentile of particles having a certain maximum diameter.For example, in a particle population having a target size of 0 to 18microns, for instance, the median maximum diameter (D50) may be 2.5microns, the largest diameter in the 99^(th) percentile of thepopulation (D99) may be 16 microns, and the largest diameter in the1^(st) percentile of the population (D1) may be 0.1 microns.

In accordance with the present invention, certain nepheline syeniteparticle systems with particular size distributions and characteristicshave been discovered. The preferred embodiment nepheline syeniteparticle systems are a 4×15 system, a 5×15 system, and 6×15 system.These systems exhibit surprisingly and unexpected beneficial physicalproperties including, but not limited to, reduced abrasiveness, reducedgloss, reduce friction, lower oil absorption, or higher loading, betterrheology and lower thermicity. Tables 1-3 set forth below, presenttypical, preferred, and most preferred values for the D1, D50, and D99size characteristics of initial embodiments of nepheline syeniteparticle systems in accordance with the present invention. All particlesizes noted are in microns.

TABLE 1 4 × 15 Embodiment Particle System D₁ D₅₀ D₉₉ Typical 0.9-3.77.9-9.7 14.3-17.1 Preferred 1.3-3.3 8.3-9.3 14.7-16.7 Most Preferred1.8-2.8 8.8 15.2-16.2

TABLE 2 5 × 15 Embodiment Particle System D₁ D₅₀ D₉₉ Typical 3.3-6.18.4-10.4 14.6-17.5 Preferred 3.7-5.7 8.9-9.9  15.1-17.1 Most Preferred4.2-5.2 9.4 15.6-16.6

TABLE 3 6 × 15 Embodiment Particle System D₁ D₅₀ D₉₉ Typical 3.1-5.99.1-11.1 16.5-19.4 Preferred 3.5-5.5 9.6-10.6 16.9-18.9 Most Preferred4.0-5.0 10.1 17.4-18.4

In one aspect, the present invention relates to particle systems ofnepheline syenite having particular size ranges which exhibit unique andunexpected properties. The nepheline syenite particle systems have arelatively small particle size for the upper size limit i.e. the powderis “ultra-fine”, and a relatively “tight” particle size distribution.For example, in a preferred embodiment particle system, the system has amedian or D50 size of 8-11 microns, a lower or D1 size of 2-5 microns, aD5 size of 4-7 microns, a D95 size of about 15 microns, and an upper orD99 size limit of 15-20 microns. The term D95 having a target of “about15 microns” may have a range of up to about 17 microns.

Yet another object of the present invention is the provision of athermal film using the novel filler powder, preferably nepheline syenitepowder, which powder has the characteristics mentioned above.

Another object is provision of an ultra-fine powder used for a filler,which filler has a controlled minimum and maximum particle size toproduce a tailored PSD curve. Such filler is formed from naturallyoccurring rock formations, but preferably nepheline syenite.

These and other objects and advantages are part of the disclosure andwill become more apparent in the following description taken togetherwith the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a greenhouse illustrating a canopy ofthe type using a thermal film to control the cooling temperature withinthe greenhouse;

FIG. 2 is an enlarged schematic representation from the circular portionin FIG. 1 graphically illustrates the intended function and purpose of athermal film;

FIG. 3 is a flow chart schematically illustrating the first preferredembodiment of the method for producing the novel ultra-fine nephelinesyenite powder;

FIG. 4 is a block diagram of a method of producing the novel nephelinesyenite powder;

FIG. 5 is a block diagram of the method of producing one version of theultra-fine nepheline syenite powder of the present invention where thefeedstock has the desired controlled maximum particle size;

FIG. 6 is a block diagram schematically illustrating a method ofproducing a version of the ultra-fine nepheline syenite powder;

FIG. 7 is a table of the target particle sizes of several samples ofultra-fine nepheline syenite powder, including nepheline syenite powderin accordance with the present invention and setting forth the particlesize distribution between D1 and D99.9 where the target values are D5and D95 of the samples;

FIG. 8 is a PSD curve of the “bell curve” type illustrating anultra-fine nepheline syenite powder with a controlled minimum grain sizeof 4-6 microns as discussed in FIG. 7 with the relationship with theinfrared light wave length spectra and showing the maximum nodes of thesamples;

FIG. 9 is a schematic graph illustrating samples of the presentinvention produced by a method where the novel nepheline syenite powderis formed by merely removing the tail end of the nepheline syenitepowder feedstock;

FIG. 10 is a graph similar to FIG. 9 showing powder samples (12) and(13) produced by the preferred method of practicing the presentinvention;

FIG. 11 is a type of PSD curve showing tailored particle sizecharacteristics of samples (9)-(11) which is similar to the other typeof PSD curve illustrated in FIG. 8, which is a “bell” curve revealingthe maximum node of the samples;

FIG. 12 is a graph of the average contrast ratio of black and white testpanels having coatings with powder fillers made from two preferredembodiments of the present invention;

FIG. 13 is a graph of 20° gloss of powder coatings with fillers madefrom two preferred embodiments of the present invention;

FIG. 14 is a bell curve type of PSD curve comparing the preferredembodiment of the present invention with the closest existing nephelinesyenite powder;

FIG. 15 are several “bell” curve type PSD curves for nepheline syenitepowder now used as fillers in thermal film and showing the distinctionbetween these curves and the corresponding curve of the preferredembodiment of the invention illustrated in FIG. 14;

FIG. 16 is a graph for defining “thermicity” property as used indescribing the present invention;

FIG. 17 is a graph showing the FTIR spectra for a film using theexisting powder shown in FIG. 14 and illustrating the range of infraredwave length used in tailoring the particle size profile in the presentinvention;

FIG. 18 is a plot of the thermicity for a film using the preferredtailored nepheline syenite powder compared to the thermicity of a filmusing the closest existing nepheline syenite powder, i.e. Minbloc HC1400;

FIG. 19 is a table of the thermicity of a film using the preferred novelnepheline syenite powder and the thermicity of the same film using theclosest nepheline syenite powder as shown in FIG. 14;

FIG. 20 discloses curves illustrating the transmittance of certainexamples of the present invention compared to prior art fillers M4000,Glomax and Polestar as now used in thermal films;

FIG. 21 is a block diagram of a second preferred embodiment of aninventive method for producing ultra-fine nepheline syenite powderhaving the characteristics of the novel powder of the present invention;

FIG. 22 is a schematic diagram of an opposed air jet mill of the typeused in practicing the method described in FIG. 21;

FIG. 23 is a Table of particle size analysis for an ultra-fine nephelinesyenite powder targeted as a 5×15 powder showing maximum and minimumparticle sizes;

FIG. 24 is a block diagram schematically illustrating the secondpreferred embodiment of practicing the present invention like theembodiment of FIG. 21 and the practical alternative to the embodimentsof the first preferred method, as described in FIGS. 3-6;

FIG. 24A is a particle size distribution curve for a feedstock used inthe second preferred embodiment as illustrated in FIG. 24;

FIG. 24B is a table representing the particle size distribution data setforth in the graph of FIG. 24A;

FIG. 25 is a table defining the parameters for operating the fluidizedbed jet mill used in the practice of the second preferred embodimentillustrated in FIG. 24;

FIG. 25A is a particle size distribution curve for the output of themill and classifier used in practicing the second preferred embodimentof the method described in FIG. 24;

FIG. 25B is a table of the particle size distribution curve as shown inFIG. 25A of the product having its maximum grain size controlled to atarget size of 15 microns;

FIG. 26 is a table of the type disclosed in FIG. 25 illustrating theoperation of the air classifier in the second preferred embodiment ofthe present invention showing in FIG. 24;

FIG. 26A is a particle size distribution curve of the product issuingfrom the air classifier stage of the method disclosed in FIG. 24 withthe minimum grain size reduced to the targeted level of 5 microns;

FIG. 26B is a table of the particle size distribution curve set forth inFIG. 26A to define the product as produced by the second preferredmethod as described in FIG. 24; and;

FIG. 27 is a specification sheet for the novel powder product by themethod defined in FIGS. 23-26B.

Having thus defined the drawings, further features of the invention willbe hereinafter described.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings wherein the showings are for the purposeof illustrating the preferred embodiments of the invention only and notfor the purpose of limiting same, FIG. 1 shows greenhouse GH having aninternal growing chamber 1 with a transparent structure called the“greenhouse cover film” or canopy 2 to allow sunlight into chamber 1 forthe purpose of growing plants PT. In accordance with standard practice,canopy 2 includes thermal film TF, as best shown in FIG. 2. Although thefilm is described for use over a greenhouse, it can be used in various,well known applications. The thermal film has an outside surface O andan inside surface I. Visible light rays L are transmitted through filmTF into chamber 1 for the purpose of promoting photosynthesis tofacilitate growth of plants PT. The amount of heat energy transmittedfrom the outside to the inside of film TF is referred to astransmittance that will be explained in more detail with respect to FIG.20. During the day, radiation L from the sun passes thermal film TF ofgreenhouse GH. At night, heat in chamber 1 is dissipated as infraredrays IR passing outwardly through film TF. The amount of heat loss isillustrated schematically as rays IR′. It is necessary to maintain heatin chamber 1; therefore, it is essential that the heat loss by radiationthrough the film is minimized and reflected back into the chamber asindicated by rays IR″. Thermicity is the fraction of infrared light inthe range of 7-14 microns that pass outwardly from chamber 1 throughfilm TF as shown in FIGS. 1 and 2. This fraction can be measured withthe FTIR spectrometer. In FIG. 16 the fraction that passes is Ai and thetotal amount of infrared radiation is Ao, which is the total area from7-14 microns. Thermal film TF now includes fillers F in fine powder formto reduce the cost of the film. These fillers also have the tendency toreduce light passing through the film and to increase the amount ofreflective infrared energy to hold the heat within greenhouse GH. Thepresent invention is directed to a novel ultra-fine powder having acontrolled minimum particle size D5 and a tailored particle sizeprofile. This film is specifically tailored to be filler F in thermalfilm TF. “Ultra-fine” indicates that the maximum grain size D95 is lessthan about 20 microns. By using nepheline syenite powder there is anincreased transmittance so that more visible light or daylight entersthe greenhouse. More light increases the photosynthesis in the growingchamber. By using an ultra-fine nepheline syenite powder, as in thepresent invention, higher loadings (5-25%) can be employed withoutsacrificing too much visible light or heat energy passing through thefilm. Consequently, thermal film TF using ultra-fine nepheline syenitepowder, especially the powder of the present invention, can be madecheaper since the resin cost are more than the filler cost. The fillerhas the attributes of “ultra-fine” nepheline syenite powder. Thethermicity of highly loaded filled films is reduced to decrease theamount of heat energy lost when sunlight is no longer creatinggreenhouse heat. The present invention relates to the nepheline syenitepowder that is “ultra-fine” and results in a film having a hightransmittance even with high loading and a low thermicity to maintainthe heat within the greenhouse. This invention relates to the art ofnepheline syenite powder, particularly to an “ultra-fine” nephelinesyenite powder which has a controlled maximum grain size or particlesize D95 of about 15 microns and a controlled minimum grain size orparticle size D5 at a level in the range of 4-7 microns. The concept ofcontrolling the minimum grain size is novel in the nepheline syenitepowder art or technology. However, the present invention goes beyondthis novel concept and increases the overall advance of the tailoredultra-fine nepheline syenite powder to allow increased transmittance ortransparency and decreased thermicity for the film in which the novelpowder is used as a filler. The development and definition of theultra-fine nepheline syenite powder with a tailored particle sizeprofile and methods of producing such novel powder are hereinafterdescribed utilizing the drawings, which showings are not intended to belimiting, but only illustrative.

The invention involves a novel ultra-fine nepheline syenite powderhaving a very narrow particle size distribution so that distinct andrepeatable physical enhancements are created in thermal films. The novelultra-fine nepheline syenite powder has a controlled minimum particlesize of 5-7 microns. This controlled minimum particle size lowers oilabsorption, allows higher loadings in thermal films, and produces higherclarity films with less yellowing and lower thermicity. Indeed, theembodiment of the invention having a minimum grain size D5 of 4-7microns and a maximum grain size D95 of about 15 microns improvesrheology and reduces thermicity of thermal films.

The inventive aspect of the novel ultra-fine nepheline syenite powder isthat the minimum particle size or grain size D5 of the produced powderis controlled to a value in the range of about 4-7 microns. These aretarget values which are used to define the product even though theminimum grain size or particle size may vary slightly from the targetedvalue since control of a particle size of this low magnitude results ina certain size deviation. Control of the minimum grain size to a levelof 4-7 microns is unique. Such controlled particle size reduces gloss,improves clarity and reduces yellowing. A thermal film using the novelnepheline syenite powder having a controlled minimum grain size of 4-7microns has a low gloss or a matte finish. The Mohs hardness ofnepheline syenite powder is in the range of 6.0-6.5 which is quite hardfor fillers and imparts hardness to the coating or film. Thischaracteristic of nepheline syenite powder together with the fact thatnepheline syenite powder has virtually no free silica makes the powderquite useful in both coatings and thermal films. Such powder can be usedat higher loading levels, such as 20-25% by weight, to reduce theoverall cost of the film. This capability is a further advantage ofusing the present invention. The control maximum grain size reduces theabrasive properties of the new nepheline syenite powder as it is used toenhance the physical properties of the films, as so far described. Afterextensive research and development it has been discovered that the novelultra-fine nepheline syenite powder can be produced by two preferredtypes of powder production methods, as so far described and as set forthin more detail in the various drawings of this application. The firsttype of method for producing the desired ultra-fine nepheline syenitepowder of the present invention has been so far described and isillustrated in more detail in FIGS. 3-11. The type of second preferredproduction method has also been described generally and is presented inmore detail in FIGS. 21-27 and characteristics and properties of thenovel powder are disclosed in FIGS. 12-20.

Novel Ultra-Fine Nepheline Syenite Powder

As so far described, the present invention relates to an ultra-finenepheline syenite powder that is tailored for use in thermal film asdescribed in connection with FIGS. 1 and 2. Preferred samples of thisnovel powder are illustrated in the table of FIG. 7 wherein samples(9)-(11) produced in accordance with the present invention are set forthwith respect to the tailored grain size profile of the powder. Thepowder is “ultra-fine” with a particle size D99 less than about 20microns. An ultra-fine nepheline syenite powder with a controlledmaximum grain size inherently has good transmittance. The opticalproperties of nepheline syenite allows for high loading. In the samples,the controlled minimum grain size D5 has a targeted particle size of 4microns, 5 microns or 6 microns. Production methods for these novelnepheline syenite powders tailored for thermal film will be explainedlater. As illustrated in FIG. 8, the particle size distribution curve ofthe samples in FIG. 7 are provided as “bell” curves 9, 10 and 11,respectively. The particle size profiles are concentrated in the area ofthe infrared spectra defined by 7-14 microns. The mid range of infraredenergy is about 2.5 microns to 25 microns as designated in FIG. 8. Inaccordance with the invention, the novel powder of the invention isconcentrated in the very limited range of 7-14 microns. This is therange that corresponds to the infrared wave length that definesthermicity, i.e. in the middle of the mid range. This is a furtherdistinguishing feature of the present invention. In summary the particlesize tailored nepheline syenite powder has a controlled maximum grainsize D95 of about 15 and a controlled minimum grain size D5 at a levelin the range of 4-7 microns. The maximum particle size node is in therange of 7-14 microns. Samples (9)-(11) are produced from apre-processed nepheline syenite powder processed to have a maximum grainsize D95 substantially greater than 20 microns by controlling both themaximum grain size D95 and the minimum grain size D5 as recorded in FIG.10. Of course, in accordance with an aspect of the present invention thenovel nepheline syenite powder can be produced by starting with orprocessing a nepheline syenite powder to have a controlled maximum grainsize D95 of about 15 microns. Then, the process for making the novelnepheline syenite powder having a controlled minimum grain size D5 of4-7 microns merely removes particles having a grain size less than theselected minimum targeted D5 particle size. This production concept isdisclosed by the grain size profiles disclosed in the table of FIG. 9.In both instances, the desired novel nepheline syenite powder has a PSDcurve such as shown in FIGS. 8 and 11 wherein the D5 grain size is inthe general range of 4-6 microns and the maximum controlled grain sizeD95 is about 15 microns. The curve of FIG. 11 corresponds to the curvesof FIG. 8. Both types of curves are particle size distribution curves,with the curve of FIG. 8 being a “bell” shaped concept and the curve ofFIG. 11 being a percentage distribution type PSD curve. These two typesof curves both illustrate the preferred novel ultra-fine nephelinesyenite powder samples (9)-(11) of FIG. 7. Having thus described thetailored ultra-fine nepheline syenite powder of the present invention asused for a thermal film described with respect to FIGS. 1 and 2, detailsof certain methods and characteristics learned and developed in thedevelopment of the novel powder are hereinafter described. Fillers forthermal film control the thermicity and transparency properties to thethermal film used to construct greenhouses as shown in FIG. 1 and FIG.2. Films TF allow visible light to pass a limited heat loss during nighttime while reflecting back infrared radiation at night. The films aretypically polyethylene or ethylene vinyl acetate resins. A range offiller powders have been used in thermal films; however, the presentinvention relates to nepheline syenite which has substantially no freesilica and more particularly to tailoring the particle size distributionor profile for the nepheline syenite powder. The thermal performance ofthe filler in the resin is referred to as thermicity of the film, whichis the fraction of infrared light that passes the film in the range of7-14 microns as described in FIG. 16 and as measured for a specificprior art filler Minbloc HC1400 in FIG. 17. The basic advantage of thepresent invention is the provision of a nepheline syenite powder havinga controlled maximum grain size and a controlled minimum grain size. Inaccordance with this basic novelty, the maximum grain size of theinvention is about 15 microns and the minimum grain size is a value inthe range of 4-7 microns. This tailored grain size profile providesexcellent transmittance, as shown in FIG. 20, a reduced tendency tosettle during production of the film and less wear on equipment used inmaking the film. By controlling the minimum particle size D5, the rangeof particle size distribution is generally no more than 10-12 microns sothat the novel powder has a profile with a narrow particle size span andwill, thus, perform consistently when mixed with resin to produce athermal film. Such advantages of the novel concept of controlling boththe maximum grain size and the minimum grain size in a powder which isindeed “ultra-fine” (with a maximum grain size of less than about 20microns) is enhanced by the added feature of reducing the transmicity byconcentrating the tailored particle size distribution in the wave lengthof infrared light corresponding with a spand or spectra of 7-14 microns.Thus, the present invention relates to the concept of a tailorednepheline syenite powder which is ultra-fine, has controlled maximumgrain size, has controlled minimum grain size and has a distributiongenerally in the range of 7-14 microns. The tailored particle size ofthe ultra-fine nepheline syenite powder also creates a narrow particlesize distribution in the range of about 10-12 microns.

The new nepheline syenite powder greatly enhances the performance of athermal film. The preferred implementation of the invention is a powdersuch as sample (10) of FIG. 7 having a maximum grain size D95 of 15microns and a minimum grain size D5 of 5 microns. The transmittance, orthe ability to allow any incoming light, is graphically illustrated inFIG. 20 and compared with prior art powder fillers Glomax, Polestar,M4000 and Minbloc HC1400. Minbloc HC1400 is the prior nepheline syenitepowder improved by the new powder. The transmittance of the preferredimplementation of the present invention is generally the same as MinblocHC1400. Transmittance of the thermal films is important for wave lengthsin this range because 300 nm is the cut-off for solar radiation.Consequently, transmittance only up to about 300 nm wave lengthindicates how much solar light passes through the film. Nephelinesyenite is more transparent over the whole range of radiation emitted bythe sun, including the important PAR range (photosynthetically activeradiation), which is the radiation crops use for photosynthesis. In thiswave length range, the nepheline syenite powders are substantiallysuperior to other prior art fillers. The preferred 5×15 powder is aboutthe same as Minbloc HC1400 and the embodiment 6×17 is in the samegeneral area of high transmission. Nepheline syenite powders includingthe embodiments 5×15 and 6×17 allow light energy transmitted into thegreenhouse substantially better than fillers which are not nephelinesyenite powder. Thus, transmittance of the novel powder is high.Thermicity and transmittance of a film is calculated and determined in amanner described in FIGS. 16 and 17. By this standard procedure, athermal film using the novel powder has been found to have a quite lowthermicity as recorded in FIGS. 18 and 19. The parameter is in theneighborhood of about 19%, i.e. less than 20%. Thus, the presentinvention has the advantages of controlled minimum grain size with a lowspread between the maximum controlled grain size and the minimumcontrolled grain size. The controlled particle size spread is between10-12 microns. This is an advantage over all prior art fillers forthermal films.

A film using the novel nepheline syenite powder of the present inventionhas a high transmittance as shown in FIG. 20 and a low thermicity asdisclosed in FIGS. 18 and 19. Thermal films tested for the results inFIGS. 18 and 19 were compounded from LDPE resin having a thickness of100 microns. These films were prepared with fillers formed from powdershaving the novel concept of controlling the particle size profile. Theloading was 10%. These films used the novel powders and are identifiedin FIG. 19 as NS 6.0×16.5 (6×17), NS 6.0×16.5 (6×17), NS 4.9×15.2 (5×15)and NS 5.1×15.6 (5×15). The thermicity of these films using thepreferred embodiment 5×15 and the alternative embodiment 6×17 had ameasured thermicity of about 19%, i.e. less than 20%. This value iscompared to the measured thermicity of about 21% for a film using theclosest prior filler as reported in the table of FIG. 19. This is asubstantial reduction of the thermicity of a film using the presentinvention when compared to a film including the closest prior artMinbloc HC1400. The results of the thermicity measurements are reportedin the plot of a fitted model based upon the D50 particle size as shownin FIG. 18. Consequently, the thermicity of a film using the presentinvention is substantially less than 20%. This compares with thethermicity of film using prior nepheline syenite Minbloc HC1400 which issubstantially greater than 21%. This comparison is shown in FIGS. 18 and19. The thermicity of the film is improved by optimizing the particlesize distribution to create a tailored particle size profile.

Light transmission is affected by both light absorption and scattering.These two properties are not easily distinguished. The particle sizegreatly affects scattering. By adjusting the particle size, scatteringand thereby light transmission can be controlled in accordance with thepresent invention. Current grades of nepheline syenite powder produceresults in a filler for thermal film that has a size distribution thatis very wide and skewed toward the large particle size. For instanceMinbloc HC1400, as shown in FIGS. 14 and 15, has a size ranging from D5of 2 microns to a D95 particle size of over 15 microns. There is amaximum mode above 10 microns and about 15 microns as shown in FIGS. 14and 15. The improved thermicity of a film using the present invention isobtained by the tailored particle size profile with a particle size PSDcurve that matches a 7-14 microns wave length. This is the generalcenter of the wave length mid-range and increases the energy reflectedby the thermal filler of the film. Nepheline syenite with a particlesize distribution of D5 equals 5 microns and D95 equals about 15microns. This film has a better thermicity than a film using theparticle size distribution currently available in other nephelinesyenite powders. Thus, high transmittance and other advantageousproperties of using nepheline syenite powder as a filler for thermalfilms are combined with the advantages of (a) controlled minimum grainsize and (b) narrow particle size range to reduced the thermicity of thefilm. In FIG. 14 where the 5×15 curve is compared to the Minbloc HC1400curve the difference between existing nepheline powder and the newpowder is apparent.

The improvement in thermicity of the film is only a few percent, but itdoes result in a thermicity that is on par with or less than thethermicity of films using other industrial leaders. In a test with 10%loading of the 6×17 powder of the invention, the thermicity was 19%.Minbloc HC1400 produced a film having a thermicity over 21% andCristobalite produced a film having a thermicity of about 22%. Theclosest non-syenite or nepheline syenite was Polestar to produce a filmhaving a thermicity of about 19%, but having a low transmittance asshown in FIG. 20, so it blocks energy in both directions. The inventionproduces a film with low thermicity with a high transmittance whilegiving better optical properties (See FIGS. 12 and 13) and lower orequal transition metal content. The haze for the 5×15 preferred versionof the present invention is about 60 and the clarity is about 24-25.This full clarity and low haze together with the transmittance andthermicity of film using the present invention makes the presentinvention a uniquely different and superior filler for thermal films. Itmaintains the advantages of nepheline syenite type of powder. As shownin the table of FIG. 19 and in FIG. 20 an alternative version of thepresent invention having a distribution of 6 microns for D5 and 17microns for D95 has equally reduced thermicity to the 5×15 preferredembodiment of the present invention. Thus, the term “about 15 microns”which was the preferred targeted maximum particle size has in practiceexpanded to mean a controlled maximum grain size D95 which may extend toabout 17 microns. The embodiment of the invention which has a minimumgrain size of 6 and a maximum grain size of 17 is produced by using thetargeted values set forth in FIG. 7 with a slightly expanded“controlled” maximum grain size. This expanded targeted grain size forthe 6×17 powder is not preferred over the 5×15 powder.

In summary, the present invention relates to an ultra-fine nephelinesyenite powder having the distribution such as generally shown in FIG. 8and illustrated schematically as curve 5×15 in FIG. 14. This curve ofthe preferred embodiment in FIG. 14 is compared to the curves for thethree commercial Minbloc powders shown in the distribution curve of FIG.15. The difference of the invention is the distinction between the curveshown in FIG. 14 and FIG. 8 as compared to the nepheline syeniteparticle distribution “bell” curve shown in FIG. 15. The inventionemploys the advantages of ultra-fine nepheline syenite powder with amaximum particle or grain size of less than 20 microns, together with acontrolled maximum grain size and a controlled minimum grain size. Thisproduces a narrow range of particle size to produce consistency whileobtaining the advantage of making the nepheline syenite powderultra-fine. Furthermore, it has been found that the thermicity can beimproved without affecting the transmittance of the nepheline syenitepowder by tailoring the nepheline syenite powder as shown in FIGS. 8 and14. The thermicity is a known parameter having the characteristics asshown in FIG. 16. FIG. 17 utilizes this same mathematical relationshipthat is illustrated with respect to a nepheline syenite powder fillersuch as Minbloc (HC1400). The portion of the transmittance wave formcurve between 700 and 1400 wave numbers for the resin is used todetermine the thermicity of the resin or film using the nephelinesyenite powder and loaded to about 10% for the resin of FIG. 17. FIGS.18 and 19 show the thermicity values of thermal films prepared with thepreferred nepheline syenite powders and prior art Minbloc HC1400powders, all having 10% loading.

The invention of the novel nepheline syenite powder indicated that theperformance of the filler for the thermal films depends upon theparticle size profile. The nepheline syenite powder of the presentinvention was classified by a Nisshin Engineering classifier Model TC-15NS as schematically illustrated in FIG. 3. The particle size forclassification is computer controlled by adjusting the rotational speedof the disk and the air flow over the disk. When setting a specificsize, three fractions are corrected. The first fraction is larger thanthe set value and is indicated to be the classifier fraction directed byline 52 to corrector 50. The second fraction is a value smaller than theset value and is termed the cyclone fraction. This is directed tocorrector 40. The waste fraction contains mostly very fine particles butalso large particles that were not corrected by the classifier disk.This fraction is discarded at corrector 60. By controlling first themaximum particle size then the minimum particle size to defined values,the resulting novel powder produces a film having thermicity which isreduced. The powder has a tailored particle size profile to have all theadvantages of a narrow spread between the maximum and minimum particlesizes and an improvement in the scattering of light by matching theparticle size with the range of infrared radiation to be scattered. Thethermal performance of the nepheline syenite of the present inventionwas also improved by about 10% by creating the powder with a D50 grainsize of about 8-10 microns.

To test the novel nepheline syenite powder, it was compounded with a lowdensity polyethylene resin. Ethylene vinyl acetate resin is a commonthermal film to be compounded in the same manner. The loading of thenovel filler powder in the resin for the test was 10%; however, theloading can be between 5 and 25 percent. The thermicity of the film wasdetermined in the range of 7-14 microns. It was found that theperformance of the nepheline syenite powder depend upon the PSD so thatthe particle size profile is skewed toward a smaller grain size in thegeneral range of 7-14 microns as shown in FIG. 8. A key property of thenew nepheline syenite powder is the thermicity of the resin or filmusing the powder. It was found that the thermicity was indeed a functionof the particle size profile. The thermicity reported in FIG. 18utilizes the D50 particle size to plot the thermicity of a film usingthe invention and the closest prior art. The lowest thermicity used increating the plot of FIG. 18 was found when the D50 value of the presentinvention was about 8-10 microns as reported in the table of FIG. 19. Toestablish the advantage of the present invention a standard nephelinesyenite powder Minbloc HC1400 having a profile as shown in FIGS. 14 and15 was merely modified to remove the tail at the smaller particle sizeof this commercial product. This act alone, without the novel tailoringof the invention, was found to reduce the thermicity of a film using theresulting powder. Consequently, a major contributor to a reducedthermicity is the removal of small particles to “control” the minimumparticle size D5 to a value in the range of 4-7 microns. All the samplesof the present invention use this basic concept as not heretoforeemployed in making nepheline syenite powder tailored for fillers inthermal films.

Thermicity and transmittance of a film are positively correlated formost fillers not formed from nepheline syenite powder. Lower (andbetter) thermicity is found in films that have lower transmittance. Athermal film that passes less daylight passes less infrared light aswell. However, the 5×15 preferred embodiment of the present inventionproduces a film having high transmittance and still very goodthermicity. For instance, this preferred embodiment produces a filmhaving higher transmittance than film using Polestar and yet has atleast as low thermicity. The haze and clarity of the resin including thefiller is controlled by scattering. This function does not correlatewith thermicity. Furthermore, a weak negative correlation is foundbetween the particle size D50 and clarity. Larger particles cause lowerclarity. However, no correlation of the transmittance or haze with theD50 value was found during testing. Consequently some properties of aresin using the particular fillers are correlated and others are not.Optical properties are important for performance of the film having afiller. For optimum crop growth, at least 80% of the sunlight needs togo through the thermal film. This factor limits the maximum fillerloading that can be used. However, transmittance and the function ofloading could not be used to estimate the maximum possible loading. Ithas been found that the loading of the filler used in the presentinvention can be higher than most other fillers not formed fromnepheline syenite powder. Testing and producing of the powder inaccordance with the present invention has also revealed that nephelinesyenite powder with a D50 value ranging from 8-10 microns is beneficial.It has also been found that if the minimum particle grain size is about5-6 microns and the maximum particle grain size is about 15-17 microns,the optimum results are obtained. This slight increase in the targetedor controlled particle size is included in the definition of “about 15microns”. Shifting the preferred targeted maximum size slightly keepsthe particle size profile in the area shown in FIG. 8 and merely skewsthe curves 9, 10 and 11 in FIG. 8 slightly to the right. The particlesize profiles are still concentrated in the wave lengths of 7-14microns.

The novel nepheline syenite powder having a controlled maximum grainsize D95 of about 15 microns and a controlled minimum grain size D5 inthe range of 4-7 microns has been produced by using a clarificationmethod shown in FIGS. 3-6 or a milling and clarification method asdescribed with respect to examples described in FIGS. 21-26. When theclassification method is employed, it has been found that a version ofthe powder having a maximum grain size of about 15 microns and a minimumgrain size of 5 microns with the D50 grain size of 10 microns has beenproduced by a multi-stage operation of the classifier shown in FIG. 3.In the first stage, a coarse cut is made with the classifier set at 13microns. This sets the maximum grain size D95. Thereafter, thepre-processed powder from the first run or “cut” of classifier 10 isprocessed by the classifier again with the classifier set at 5 microns.This process was repeated three times so the resulting “controlled”minimum grain size D5 was 5.3 microns the maximum grain size D95 was15.2 microns. The D50 particle size was 9.31 microns. This process wasused for producing sample (10) set forth in FIG. 7.

The ultra-fine powder, as described, primarily utilizes a syeniticmaterial or composition, such as nepheline syenite; however, it has beenfound that the advantages of the invention, as defined herein, areobtainable by using natural occurring mineral or rock materials having ahardness above 5 on the Mohs scale or naturally occurring mineral orrock material with a refractive index in the range of 1.4 to 1.6 and,indeed, preferably 1.46 to 1.56. The invention using either of these twotypes of material is still ultimately an ultra-fine powder having acontrolled or “engineered” particle size distribution in the definedrange to reduce the thermicity of a thermal film using the ultra-finepowder to a value less than about 20%. When the invention is practicedby utilizing one of several defined hard mineral or rock materials, thenovel powder is produced as long as the powder has the definedengineered particle size distribution. As is known, a hard material isdefined as a Mohs hardness of 5 or higher. Feldspar has a Mohs number ofabout 6 and quartz has a Mohs number of about 7. Various naturallyoccurring materials having the correct controlled, engineered particlesize distribution will produce a low thermicity, when used in thethermal film and will have the other advantages mentioned above whenused in other applications.

As indicated above, the naturally occurring material forming thefeedstock to produce the ultra-fine powder of the present invention canbe selected according the Mohs number or its refractive index, so longas the novel controlled PSD is imparted to the powder made from thematerial. Powder made from hard material has other applications besidesthermal film. Material selected by its refractive index is materialparticularly useful for thermal film and clear coatings. The inventionis not limited to a selected type of material, although the particular,defined types of materials are further definitions of the invention. Thetypes of materials are aspects of the invention, as defined in theappended claims and disclosed in the statements of invention and theobjects of the disclosed invention.

When the feedstock material is selected by its Mohs number, it has beendetermined that such material can be selected from the class comprisingnepheline syenite, feldspar, silica, quartz, cristobalite and tridymite.However, when the feedstock material is selected based upon the range ofthe refractive index, it has been determined that such material can beselected from the class comprising silica (including ground natural anddiatomaceous), cristobalite, feldspar, quartz, nepheline syenite,kaolin, alumina triydrate, talc, attapulgite, pyrophyllite, calciumhydroxide, magnesium hydroxide and hydrotalcite. The starting materialsare preferably selected from the class consisting of silica (includingground natural, diatomaceous) cristobalite, feldspar, quartz, nephelinesyenite, kaolin, talc, attapulgite and pyrophyllite. These materialshave been processed as described herein.

In addition, research and development work in producing and perfectingpowder with the controlled particle size distribution has resulted indevelopment of novel manufacturing methods for some of the feedstockmaterials. Thus, methods of producing the ultra-fine powder are definedby the several appended claims of this application. These appendedclaims constitute a part of the disclosure of the invention.

Classification Method FIGS. 3-11

To produce the narrowly sized nepheline syenite powder of the presentinvention, the first preferred type of production method involves theuse of air classifiers to control the minimum grain size of thenepheline syenite powder. Control of the minimum particle size is a newconcept in the nepheline syenite powder art of the nepheline syeniteindustry. The initial research and development project resulted inmethod A using a Nissin Engineering Turbo Classifier Model TC-15-N-S asshown in FIG. 3. It was discovered that this air classifier operated ina unique manner could produce the desired nepheline syenite powdersconstituting the inventive aspect of the present invention. Classifier10 is equipped with a microprocessor that calculates operatingconditions based upon the minerals specific gravity and the cut offpoint “x” for producing one extreme of the desired ultra-fine nephelinesyenite powder. Method A disclosed in FIG. 3 utilizes the TurboClassifier 10 in which a feedstock comprising a pre-processed nephelinesyenite powder or a powder from a prior run of the classifier isintroduced as indicated by feedstock supply or block 12. In thepreferred embodiment, pre-processed nepheline syenite powder isintroduced into classifier 10 as indicated by line 14. In practice, theinitial feedstock from supply 12 through line 14 is a powder made fromnepheline syenite or another naturally occurring rock or mineral withouta significant amount of free silica. The feedstock has a controlledmaximum particle size or grain size greater than 20 microns andpreferably in the range of 20-150 microns. This pre-processed nephelinesyenite powder with a controlled maximum grain size is introduced intoclassifier 10 for a purpose of producing various nepheline syenitepowder with a first run having targeted maximum particle size D95distribution and then a subsequent run where “x” is the targeted minimumparticle size D5. This procedure produces samples (9)-(11), as shown inthe first column of FIG. 7. Each of these novel ultra-fine nephelinesyenite powder samples made in accordance with the present inventionhave a minimum particle size D5 in the range of 4-7. The minimumparticle size is controlled by classifier 10 as removed from collector40 as well as a maximum grain size produced in a prior run and removedfrom collector 50. This intermediate powder produced by a first runthrough classifier 10 is used for the minimum size run.

Method A using classifier 10 includes a data input block 20 where anoperator inserts the specific gravity of the nepheline syenite powder.The maximum size D95 and then the minimum size D5 are selectivelyentered as set value “x.” Data from block 20 is directed through line 22to a microprocessor stage 30. Microprocessor stage 30 sets theclassifier air flow and the rotor speed of the classifier. Selectedinformation is provided to the classifier through line 32 to operateclassifier 10 for controlling first the upper and then the lower grainsize of the final powder. During the first run the cyclone section ofclassifier 10 separated particles greater than the desired particle sizevalue x as set by microprocessor 30. This intermediate powder isdeposited into collector or block 40 through line 42. The intermediatepowder with a controlled maximum particle size is removed from collector40 and introduced into supply 12 for reprocessing by classifier 10 withset particle size “x” at the targeted minimum particle size D5. In thisprocedure the final novel ultra-fine nepheline syenite powder isdeposited into collector or block 50 by line 52. This second operationmay require more than a single pass through the classifier and theparticle size value “x” may be progressively reduced. Small fines aredischarged from classifier 10 into block 60 through line 62.

Classifier 10 employs a classifier disk in accordance with standardtechnology and a cyclone to process the feedstock entering theclassifier through line 14. See English U.S. Pat. No. 4,885,832 for arepresentative description of this known technology. Microprocessor 30controls the air for dispersion and for the classifier as indicated byblock 70. Thus, microprocessor 30 is set for a determined particle size“x” which size is controlled by the rotating rotor disk and the cycloneof the classifier. Consequently, in practice nepheline syenite feedstockis classified by the Turbo Classifier 10 using a combination of theclassifier disk and cyclone. The particle size D95 or D5 is computercontrolled by adjusting the rotational speed of the disk and the airflow over the disk. When setting a specific size, D99 or D5, threefactions are collected. The faction less than the set value “x” which isdirected to collector or block 40. The large faction greater than theset value, is separated by the disk of the Turbo Classifier 10 anddeposited “x” into collector 50. The waste faction is directed to block60 and contains mostly very fine particles but also large particles thatwere not collected by the classifier disk. This waste material isdiscarded.

Classifier 10 is set by an operator by the data input at stage or block20 to control the classifier disk and the cyclone air so that the setparticle size “x” is separated as indicated by either block 40, 50. Ifthe classifier is set to the desired targeted minimum particle size D5,the powder is collected at block 50. If the collected powder is to havea maximum grain size or particle size, it is either previously orsubsequently passed through the classifier again and the data entered atblock 20 is the maximum grain size. The powder is collected from block40. Thus, by both a lower cut and upper cut of particle size byclassifier 10, the novel ultra-fine nepheline syenite powder isproduced. Samples of the novel powder are defined by the values in FIG.7 with the PSD curves shown in FIG. 8. The novel powder for thermalfilms is “ultra-fine” nepheline syenite powder which defines a powderhaving a maximum grain size less than about 20 microns. The substantialadvantages of “ultra-fine” nepheline syenite powder have been recentlydiscovered and are known in the art, especially when the ultra-finenepheline syenite powder is used as a filler in coatings or, especiallythermal films.

Operation of method A as described is used to produce ultra-finenepheline syenite powder with various targeted sizes as set forth in thesamples (9)-(11) of FIGS. 7 and 8. The targeted sizes have resulted inthe actual particle size distributions recorded in table of FIG. 7.Method A is the first preferred embodiment of a type of processdiscovered to be useful in practicing the present invention, whichinvention relates to an ultra-fine nepheline syenite powder for thermalfilms and having a controlled minimum particle size D5 of 5-7 microns.The novel powder has a controlled maximum particle size D95 of about 15.The actual particle size distribution for targeted samples (5)-(11)described in FIG. 7, is shown in the particle size curve of FIGS. 8 and11. The powder can be made by only removing the smaller particles usinga feedstock with a D95 particle size of about 15 microns as shown inFIG. 9 or by “control” of both the D95 and D5 particle size as in FIG.10.

These preferred implementations of the present invention, samples(9)-(11) have a controlled maximum particle size of 15 microns and havethe actual grain size distribution as shown in the table of FIG. 7 andin the curves of FIGS. 8 and 11. The general range of particle sizes areshown in FIGS. 9 and 10 where the minimum size is D5 and the maximumsize is D95. The feedstock or intermediate powder has a D95 particlesize in the powder of FIG. 9. The novel concept is controlling the lowergrain size of the nepheline syenite powder to a minimum size of 4-7microns, combined with controlling the maximum particle size of thenepheline syenite powder to a size D95 of about 15 microns as in samples(9)-(11). These samples have the targeted particle sizes and the actualparticle size distribution provided in FIG. 7 and illustrated in theparticle size distribution curves of FIGS. 8 and 11. The same particlesizes are shown as the powder sizes in FIGS. 9 and 10.

In summary, method A schematically illustrated in FIG. 3 has beendeveloped to produce the novel ultra-fine nepheline syenite powder ofthe present invention wherein the minimum particle size is controlled tocreate an ultra-fine nepheline syenite powder with a maximum particlesize D95 of about 15 microns with a controlled minimum particle size D5of 4-7 microns.

Method A can be operated to produce the novel ultra-fine nephelinesyenite powder by performing the steps set forth in FIGS. 4 and 5.Method A, as shown in FIG. 3, is used to produce samples (9)-(11) asdisclosed in FIGS. 8 and 11. This method makes the powder described inFIG. 10. As shown in FIG. 4, nepheline syenite powder having a maximumparticle or grain size greater than about 30 or 40 microns is introducedas the feedstock in hopper 12 as indicated by block 100. Since thismaterial has a relatively large controlled maximum grain size, it isfirst passed through classifier 10 as indicated by block 102 to controlthe minimum particle size, represented as x, i.e. 4-7 microns.Thereafter, it is passed through classifier 10 to control the maximumgrain size y, as indicated by block 104. This procedure makes a powderas indicated by block 110. The two classifying stages are normallyreversed. The product has a minimum particle size x of 4-7 microns and amaximum particle size y of about 15 microns. A feedstock with a maximumparticle size D95 of about 15 microns can be the starting material asshown in block 112 in FIG. 5. The feedstock has the desired maximumparticle size D95 and is merely passed through the classifier set toremove the smaller particles. The minimum D5 particle size x isestablished, as indicated by block 114 of FIG. 5. This procedureproduces at collector 120 samples described in connection with FIG. 9.The maximum grain size D5 is controlled by the inherent maximum particlesize D95 of incoming feedstock. The feedstock itself has the desiredcontrolled maximum particle size of about 15 microns. Turning now to thealternative method disclosed in FIG. 6, classifier 10 is used to producean ultra-fine nepheline syenite powder by merely removing the particlesizes above a given value y from feedstock 122 as indicated by block124. Such powder at collector 130 results in creation of an ultra-finenepheline syenite powder with a controlled minimum particle size whichis a requirement of the present invention by using a feedstock alreadyprocessed to give a minimum grain size of 4-7 microns. FIGS. 4-6 aredisclosed since they represent various operations of method A by thesystem shown in FIG. 3 to make the novel ultra-fine nepheline syenitepowder.

To show properties of the invention, the nepheline syenite powderdisclosed in FIGS. 7 and 10 was formulated in a clear acrylic powdercoating. This is to determine the effect of the particle size of theinventive powder or clarity in gloss. In terms of gloss reduction andclarity the powder with a minimum particle size of 4 and a maximumparticle size of 15 (4×15) or a minimum size D5 of 6 and a maximum sizeD95 of 15 (6×15) performed the best and represent a new and novel way toreduce the gloss while maintaining good clarity. Two powders having thenovel features of the present invention were tested. The two sampleswere 4×15 and 6×15 powder. In the test procedure, coatings with variousfillers were sprayed onto cold rolled steel. Steel panels with a coatinghaving a target final thickness of 1.5-2.0 mils were produced. Thepanels with the coatings were baked at 204° C. each for ten minutes. Thecontrast ratio was determined by using black and white panels that werecoated and measured with a Macbth Coloreye 3000. The contrast ratio isindication of the difference in the respective measurement over blackand white. This measurement was used as an indicator of the haze. Thetwo new and novel nepheline syenite powders were tested in a clearpowder coating. The powders gave excellent results for both clarity andgloss. Lower gloss is a benefit because they usually have to useadditives, such as waxes to decrease the gloss. This is an importantdevelopment because maintaining clarity while lowering gloss is asignificant objective. The results of these tests are shown in FIGS. 12and 13. In summary, the novel nepheline syenite powder maintainsexcellent clarity while gloss was reduced by as much as 50% from theunfilled system. Thus, ultra-fine nepheline syenite powder with acontrolled minimum particle or grain size D5 of 4-7 microns maintainsclarity while lowering gloss. These tests merely illustrate theadditional properties of the powders invented for specific applicationin thermal films.

Milling and Classifying Methods FIGS. 21-27

As discussed previously, a preferred method of producing such novelpowder involves the use of an opposed air jet mill followed by aclassifier or an attrition mill operated in a dry mode followed by anair classifier. The dry mill grinds the incoming nepheline syenitepowder feedstock into a powder having reduction in the maximum particlesize. This is the normal operation of a mill; however, in accordanceinvention, the mill for reducing the maximum grain size is used toproduce a powder where the maximum grain size D95 is about 15 microns.Consequently, the resulting dual processed nepheline syenite powder is“ultra-fine”. This subsequently milled pre-processed powder feedstock isconverted into an intermediate powder with this controlled maximumparticle size. Then the intermediate powder is passed through an airclassifier to obtain the targeted minimum particle size D5 at acontrolled value in the range of 4-7 microns. The resulting powder isnew and is an ultra-fine nepheline syenite with both a controlledmaximum particle size D95 of about 15 microns and a controlled minimumparticle size D5 at a value in the range of 4-7 microns. This dualprocess creates a powder having the advantageous improved characteristicof the new powder, especially to reduce and control the thermicity of afilm using the ultra-fine nepheline syenite powder. Of the manytechnologies investigated to produce the new nepheline syenite powder,the first preferred implementation was the classifying method Adisclosed in FIG. 3. It has been found that the preferred commercialembodiment of the invention involves the use of a mill to dry grindnepheline syenite powder feedstock having a controlled grain sizesubstantially greater than 20 microns and less than about 150 microns.In practice the pre-processed powder has a D99 particle size of about100 microns and a D50 particle size of about 15 microns.

This second preferred embodiment of the present invention is method Bdisclosed in FIG. 21. Method B involves use of pre-processed nephelinesyenite feedstock having a controlled maximum particle size of about 60microns, as disclosed in the graph of FIG. 24A and table of FIG. 24B.The maximum particle size D99 of this feedstock is about 60 microns toproduce the controlled particle size of the nepheline syenite powder. Ina practical implementation of method B, the feedstock is merelyprocessed nepheline syenite having a particle size D95 or D99 over about20-150 microns.

Method B involves the use of an opposed air jet mill from HosokawaAlpine and sold as AFG Model 400. This opposed air jet mill 202 is thesecond preferred mill used in practicing the invention and isillustrated as the mill for method B shown in FIG. 21. Such mill isschematically illustrated in Zampini U.S. Pat. No. 5,423,490 andKonetzka U.S. Pat. No. 6,543,710, which are incorporated by referenceherein. This fluidized bed opposed jet mill use air jet mill forgrinding the feedstock. As compressed air exits internal nozzles, it isaccelerated to extremely high speeds. In expanding, the energy containedin the compressed gas is converted to kinetic energy. The velocity ofthe air exiting the Laval nozzle or nozzles exceeds the speed of sound.The air is the grinding gas. Gas and powder from the fluidized bed iscomminuted as the result of interparticle collision of the air jets,especially in the areas where opposed jets intersect. The fluidized bedopposed jet mill has a dynamic deflector-wheel classifier so thefineness of the particles is a function of the wheel speed. See ZampiniU.S. Pat. No. 5,423,490 for a jet nozzle design. The feedstock from feedinput or supply 200 is ground by mill 202 set to the targeted maximumparticle size which in the illustrated embodiment is about 15 microns.This opposed jet mill is disclosed in FIG. 22 and directs groundnepheline syenite powder through line 202 a to an air classifier 204,which classifier, in the preferred embodiment, is an Alpine Model 200ATP. Feedstock enters the classifier as the classifier air flows throughthe rotating classifying wheel. This wheel extracts fines and conveysthem by air from the classifier. The coarse material is rejected by theclassifying wheel and exits the lower discharge valve for the powderthat has a controlled minimum particle size. This air classifier is setto remove particles having a size less than the targeted minimumparticle size D5 in the range of 4-7 microns. Product passing throughlines 204 a is collected as indicated by block or collector 210. MethodB was developed for producing the novel ultra-fine nepheline syenitepowders identified as samples (9)-(11) illustrated in FIG. 7 and thesamples (12)-(13) illustrated in FIG. 10. In the representative use ofmethod B illustrated in FIG. 21, 5×15 sample (10) is produced. However,method B is also applicable for the other examples mentioned and,indeed, to produce the other samples of the present invention as setforth in FIGS. 7 and 10.

An opposed air jet mill performs the dry grinding function of block 202in FIG. 21. This device is schematically illustrated as opposed air jet220 in FIG. 22. Mill 220 accepts pre-processed nepheline syenitefeedstock from block or supply 200 and directing the feedstock intohopper 222. The feedstock has a maximum particle size previouslyimparted to the processed feedstock powder. This maximum particle sizeis in the general range of 20-150 microns. The processed feedstockenters mill 220 through feed hopper or funnel 222 and is then conveyedinto the mill by the compressed air or gas inlet 224 from a supply ofcompressed air or gas 226. To grind the incoming feedstock compressedgrinding air is introduced into the mill through inlet 230 connected toa compressed grinding air source 232. In accordance with this type ofcommercially available grinding mill, as already explained, there is agrinding chamber 240 where the feedstock is subject to high speed airjets. The chamber has a replaceable liner 242 and a grinding airmanifold or recirculating air chamber 244. Ground particles having areduced grain size from the feedstock are directed to outlet 260surrounded by a vortex finder 262. The ground particles P aredrastically reduced in size from the incoming feedstock FS. Thecommutation or grinding is performed by the opposed air jets in chamber240. In one use of mill 220, the particles exiting from outlet 260 hasthe desired maximum particle size, i.e. the targeted D95 size. Inanother use of mill 220, there is a classifier set at the maximumparticle size and the ground powder from outlet 260 is larger, but issubsequently classified to the desired maximum particle size, which isD95 equals about 15 microns or, indeed, targeted at 15 microns. In theequipment used in method B, mill 220 has a variable speed internalclassifier wheel which is adjusted to separate particle sizes less thana desired target size. The separated particles exit by gravity throughline 202 a into a collector 202 b. Particles in line 202 a shown in theillustrated embodiment of the invention have a maximum grain size of 15microns. Particles having larger particle size, but entering into theclassifier 270 from outlet 260 are directed through line 272 back intothe grinding chamber with incoming feedstock FS at funnel or hopper 222.Powder from the classifier wheel enter line 202 a and is deposited incollector 202 b. The powder has a controlled maximum particle size. Itis then bagged and introduced into air classifier 204, as indicated bydashed line 202 c. The opposed air jet mill is the preferred dry millused in practicing method B as shown in FIG. 21. An example of a runusing method B will be described in detail with respect to FIGS. 24-27.

Before a description of an implementation of method B shown in FIG. 21,a generic version of this method will be explained. A processedfeedstock with a large maximum particle size is directed into a “dry”mill. This mill can be an attrition vertical stirred dry mill in aclosed circuit or, preferably, an opposed air jet mill as used in thesecond preferred embodiment of the invention as shown in FIG. 22. Thus,the generic version of method B employs a dry mill that produces apowder having a maximum particle size D95 matching a selected maximumtargeted particle size of 15 microns. The dry mill is normally combinedwith an air classifier and has a coarse powder return to recirculate thepowder as it is being ground to the targeted maximum size. The output ofthe dry mill and/or air classifier is the intermediate powder. Thisintermediate powder is directed to an external air classifier thatremoves particle sizes less than the targeted minimum particle size D5,which is in the range of 4-7 microns. The preferred targeted size D5 is5 microns. From the external, second stage air classifier, the desiredultra-fine nepheline syenite powder is directed into a collector. Theproduct in the preferred embodiment is identified as a 5×15 powderhaving a targeted maximum particle size D95 of 15 microns and a targetedminimum particle size D5 of 5 microns. The first and second preferredmethods developed for producing this novel ultra-fine nepheline syenitepowder are the types of process disclosed as methods A and B. Method Bhas herein been generically disclosed to show the breadth of method usedto produce the novel nepheline syenite powder. Both methods are used toproduce the preferred samples of the novel ultra-fine nepheline syenitepowder (4×15, 5×15 and 6×15) is set forth in the curves of FIGS. 8 and11 and constituting samples (9)-(11) respectively of FIG. 7 or the 6×17version of the method as shown in FIG. 20.

Representative Run FIGS. 23-27

During the development of the novel concept of controlling the minimumparticle size D5 of an ultra-fine nepheline syenite powder to a value inthe range of 4-7 microns and maximum particle size D95 of about 15microns, several novel methods were developed and have been described.The preferred commercial implementation of the invention realizes methodB disclosed in FIG. 21. A representative test run of this method wasused to produce a nepheline syenite powder having a targeted maximumparticle size D95 of 15 microns and a targeted minimum particle size D5of 5 microns. The profile of the desired particle size distribution ofthe resulting powder is recorded in the table of FIG. 23. Method Pillustrated in FIG. 24 was used in the representative run to produce anultra-fine nepheline syenite powder having a controlled minimum particlesize of 5 microns and a controlled maximum particle size of 15 microns.The feedstock was a pre-processed nepheline syenite powder having acontrolled maximum grain size of 60-100 microns as shown in FIGS. 24Aand 24B; however, it could be other pre-processed nepheline syenitepowder. This feedstock had no controlled minimum particle size. Theparticle size distribution of the feedstock from supply 400 of method Pis shown in the graph of FIG. 24A and disclosed in the table of FIG.24B. This pre-processed feedstock is directed through line 402 to an AFGModel 400 fluidized bed opposed jet mill having an internal classifier,as indicated by block 410. Powder from the jet mill is directed throughline 412 to an Alpine Turboplex ATP Model 200 air classifier 420. Fromthe air classifier the desired product is conveyed through line 422 anddeposited in collector 430. In this representative run of method P usingthe equipment set forth in FIG. 24, the targeted minimum particle sizeD5 was x microns, which is the setting of the air classifier 420. Thecontrolled maximum particle size D95 is y microns, which is the outcomeof the jet mill 410 of method P. In the run, x equaled 5 microns and yequaled 15 microns. The Alpine AFG Model 400 jet mill with an internalclassifier produced nepheline syenite with a particle size of less than15 microns. Subsequently, particles with a size less than 5 microns areremoved by the Turboplex air classifier 420. The feedstock was manuallycharged into a K-Tron volumetric screw feeder, which conveyed thefeedstock through the double flat valves to the grind chamber of themill shown in FIG. 22. Grinding was performed by three opposed jetnozzles located on the sides of the grind chamber. The three opposed jetnozzles accelerated particles using compressed air (variable pressure)to a focal point. A vertical flow of air transported the groundparticles in a stream to the variable speed internal classifier wheelalso disclosed in FIG. 22. Coarse or unground particles were rejected bythe classifier wheel and returned to the fluidized bed for continuedgrinding. Particles small enough to be accepted by the classifier wereair conveyed to collector 202 b shown in FIG. 22. These particles weredischarged from the dust collector by way of double flat valves. Theparticle size and capacity of the test run were controlled by varyingthe grinding air pressure, novel size bed height and classifier speedusing the parameters set forth in FIG. 25. The intermediate powder inline 412 was directed to the air classifier 420 by manually charging thematerial into the hopper of a K-Tron. The feeder conveyed thisintermediate powder through a rotary air lock directly into the feedinlet air flow line. From the air flow line the intermediate powder fromthe model 400 AFG jet mill was conveyed into the classification chamberof classifier 420. As the intermediate material or powder approached theclassifier, a secondary rising air flow dispersed the material toenhance the effect of the classifier. The small fines, being lighter,floated upward to the classification wheel. The coarse material orpowder was discharged into collection drum or collector 430. Particlessmall enough to pass through the variable speed classifying wheel werediscarded. The particle size distribution (PSD) was determined usinglaser defraction (Beckman-Coulter LS 230), using Isopropyl Alcohol asthe representative test run reduced the pre-processed nepheline syenitepowder feedstock into a −15 micron intermediate material or powder forsubsequent air classification by classifier 420. The parameters andresults of the classifier stage of the test run are disclosed in FIGS.25-27.

In the representative test run, the parameters of the model 400 AFG jetmill 410 with a feed rate of about 240 lbs/hr are tabulated with theparticle size distribution also listed in the table 410 a of FIG. 25.This operation provided an intermediate nepheline syenite powder in line412 having the particle size or distribution shown in the graph of FIG.25A and the table of FIG. 25B. This intermediate material processed bythe mill and internal classifier using parameters listed in the table410 a of FIG. 25 was directed into the air classifier, which classifierwas set to parameters tabulated in the table of FIG. 26. Operating underthese parameters, the 200 ATP air classifier 420 produced the powderrecorded in the table 420 a of FIG. 26 and having the particle sizedistribution shown in the curve or graph shown in FIG. 26A and in thetable of FIG. 26B. This final product in the representative test run hada controlled maximum particle size D99 of 14.15 microns with 98.7% ofthe powder having a particle size less than 15 microns. The inventioninvolves the control of the minimum particle size which is illustratedas being 5.78 microns for D4 and with about 0.5% of the particles havinga particle size less than 5 microns. This representative test runproduced the novel ultra-fine nepheline syenite powder with a controlledminimum particle size of about 5 microns and a controlled maximumparticle size of about 15 microns and having the product specificationsof FIG. 27.

The representative test run set forth in the drawings of thisapplication related to use of method P; however, research anddevelopment is being conducted on using serial air classifiersespecially of the Alpine model 200 ATP. They have proven successful incontrolling the minimum particle size of the ultra-fine nephelinesyenite powder. Such control of the minimum particle size is unique inthe nepheline syenite powder art. Irrespective of the novelty of the newpowder, there is a substantial technological advance in the developmentand use of the method of FIGS. 21 and 24. The methods are inventions inthemselves in that they have been combined and used for controlling theminimum particle size and additionally the maximum particle size ofnepheline syenite powder in a manner not known in the nepheline syenitepowder art.

Other Devices for Making 5×15 Powder

In the initial production of the powder with a D95 size of about 15microns and a D5 size of 5 microns, several viable procedure werediscovered to produce the 5×15 powder. To make this conclusion, bulksamples of preprocessed nepheline syenite were subjected to threedifferent types of commercial ultra-fine grinding mills. These mills andvendors are listed below.

-   1. VibroKinetic Ball Mill (MicroGrinding Systems, Inc., Little Rock,    Ark.)-   2. Fluid Bed Opposed Flow Jet Mill (Hosokawa-Alpine Micron Powder    Systems, Summit, N.J.). See Konetzka U.S. Pat. No. 6,543,710 which    is incorporated by reference herein.-   3. Vertical Stirred Ball Mill (VSB-M) a.k.a. Attrition Mill (Union    Process Attritor Co., Akron, Ohio). See Szeavari U.S. Pat. No.    4,979,686 which is incorporated by reference herein.

Each mill was used to produce 5×15 microns product with a mean particlesize of about 8 microns. Distinctions in the test procedures and uniqueobstacles encountered are discussed below.

Test products were subjected to laser diffraction size analysis with aBeckman Coulter LS 13 320 Particle Size Analyzer. A “Nepheline Syenite”optical model was used instead of a “Fraunhofer” optical model. Inaddition, BET surfaces area measurements and Tappi brightnessmeasurements of each product were made. Scanning electron micrographs,SEM, of select products were also taken.

Vibro-Kinetic Ball Mill—The VibroKinetic Ball mill was operated inclosed circuit with an air classifier.

Fluid Bed Opposed Flow Jet Mill—Hosokawa-Alpine produced the 5×15 powderby grinding to <15 microns in the Jet Mill and air classifying thisproduct to remove the minus 5 micron material.

VSB-Mill (a.k.a. Attrition Mill)—This mill was used to produce the −15micron product. The Union Process Attritor Co. had no means to classify−5 micron material from the −15 micron product to make a 5×15 micronproduct. This was performed by a separate classifier.

Size distributions of the products obtained are shown in Table 5.Samples 5 and 6 exhibited a significantly “tighter” or narrowerdistribution than the other samples. Tappi brightness, L*, a*, b* colorvalues, and BET surface area values are shown in Table 6.

TABLE 4 Particle Size Analyses of Processed Nepheline Syenite SampleGrind D_(99,99) D₉₇ D₉₅ D₉₀ D₇₅ D₅₀ D₂₅ D₁ Mean 1 Vibro (−5 μm) 26.2916.48 14.30 10.29 4.90 2.32 1.05 0.42 3.93 2 Vibro (−15 μm) 61.63 22.7218.36 13.22 6.04 2.34 0.87 0.37 5.14 3 Jet (−5 μm) 5.53 4.06 3.83 3.492.92 2.29 1.71 1.10 2.27 4 Jet (−15 μm) 11.60 8.30 7.82 7.00 5.55 4.092.98 2.31 4.40 5 VSB-M (−5 μm) 2.64 1.81 1.66 1.43 0.93 0.52 0.34 0.260.69 6 VSB-M (−15 μm) 11.49 6.43 5.09 3.40 1.99 1.13 0.53 0.32 1.60

TABLE 5 Color and Surface Area Analyses of Ultra-Fine Products BET TappiSurface Sample Grind Brightness L* a* b* Area 1 Vibro (−5μ) 81.50 92.240−0.182 3.874 NA 2 Vibro (−15μ) 78.20 91.324 0.067 4.580 NA 3 Jet (−5μ)87.80 94.312 −0.066 0.452 3.5 4 Jet (−15μ) 87.85 94.075 −0.088 0.511 2.35 VSB-M (−5μ) 92.44 96.625 −0.125 0.743 17.1 6 VSB-M (−15μ) 88.41 94.660−0.195 0.996 19.0

The research and development project as described above resulted in anew level of know-how establishing that the novel nepheline syenitepowder is obtainable by proper selection of manufacturing techniques.The reported initial research and development project resulted in adiscovery of the unique process disclosed generally in FIG. 3 and thepreferred process disclosed generally in FIGS. 23-27. Selection ofpreferred methods was a major development in the nepheline syenite artand resulted finally in the ability to produce economically the novelnepheline syenite powder having a controlled maximum grain size D95 ofabout 15 microns and a controlled minimum grain size of D5 of 4-7microns, with a very narrow particle size distribution.

Powder filler samples were produced using the method of FIG. 3. A NissinEngineering, Inc. Model TC-15-NS Turbo Classifier, equipped with a finerotor for classification in the range of 2-20 microns was used. As isshown in FIG. 3, the classifier also has a microprocessor that providesautomatic calculations of operating conditions. The operator enters thedesired cut size (in microns) and the density (g/cm³) of the mineralbeing classified via a touch screen panel. Then, the microprocessorcalculates the classifier rotor speed (rpm) and classifier air required(in m³/min). As an example, a 5 microns cut with 2.7-g/cm³ nephelinesyenite requires a rotor speed of 8,479 rpm and an airflow rate of 1.2m³/min). A schematic of the classification process is shown in FIG. 3.

Particle size distribution (PSD) results of the products made with theTC-15-NS Classifier are summarized in Table 7.

TABLE 6 Actual Size Distributions of Targeted Products Actual SizeTarget Size D_(99.9) D₉₉ D₉₅ D₉₀ D₇₅ D₅₀ D₂₅ D₁₀ D₅ D₁ 4 × 15 17.1 15.714.2 13.2 11.2 8.82 6.99 5.78 5.16 2.33 5 × 15 17.1 16.1 14.6 13.7 11.79.41 7.46 6.20 5.57 4.68 6 × 15 18.6 17.9 16.1 14.8 12.4 10.1 8.02 6.465.72 4.47

The air classifier did a reasonably good job at making the target cuts.One important discovery was that the starting material greatly impactssuccess.

The Nissin Engineering Model TC-15-NS of FIG. 3 is an excellentlaboratory and small-scale pilot classifier. It is precise, accurate,and relatively easy to operate. However, the method described in FIG. 21has been discovered to be suited for production runs.

Summary Observations

Individual steps or operations in the several methods can be combinedand modified to produce the novel ultra-fine nepheline syenite powder.These combinations are novel and inventive. It is not intended that thedisclosed embodiments of the method or the specific samples of novelnepheline syenite powder are to be limited to the actual examples orsamples; but, the invention as described includes such modifications andalternatives as would occur to a person upon reading and understandingthis detailed description of the several inventions.

It is claimed:
 1. A method of producing an ultra-fine powder, saidpowder having a targeted maximum particle size D95 and a targetedminimum particle size D5 with a particle size distribution of D5 to D95of less than 12 microns, said method comprises: (a) providing a groundfeedstock formed from a naturally occurring mineral or rock materialhaving a reflective index of about 1.4 to 1.6; (b) grinding saidfeedstock in a mill; (c) classifying said mill ground feedstock with afirst classifier to produce an intermediate powder, said intermediatepowder having a targeted D95 maximum particle size with a value, whichvalue is in the range of 14-17 microns; (d) classifying saidintermediate powder through a second classifier to remove all particlesless than a targeted particle size with a value, which value is in therange of 4-7 microns to produce said ultra-fine powder having a targetedD5 minimum particle size with a selected value in the range 4-7 microns.2. The method as defined in claim 1 wherein said feedstock is a materialselected from the class comprising silica (including ground natural anddiatomaceous), cristobalite, feldspar, quartz, nepheline syenite,kaolin, talc, attapulgite, pyrophylite and tridymite.
 3. The method asdefined in claim 1 wherein said targeted maximum particle size D95 ofsaid ultra-fine powder is 15 microns.
 4. The method as defined in claim3 wherein said targeted minimum particle size D5 of said ultra-finepowder is 5 microns.
 5. The method as defined in claim 4 wherein saidfeedstock in a material selected from the class comprising nephelinesyenite, feldspar, silica, quartz, cristobalite and tidymite.
 6. Themethod as defined in claim 1 wherein said first classifier is in saidmill.
 7. A method of producing an ultra-fine powder, said powder havinga targeted maximum particle size D95 and a targeted minimum particlesize D5 with a particle size distribution of D5 to D95 less than 12microns, said method comprises: (a) providing a ground feedstock formedfrom a naturally occurring mineral or rock material having a Mohshardness of at least 5; (b) grinding said feedstock in a mill; (c)classifying said mill ground feedstock with a first classifier toproduce an intermediate powder, said intermediate powder having atargeted D95 maximum particle size with a value, which value is in therange of 14-17 microns; (d) classifying said intermediate powder througha second classifier to remove all particles less than a targetedparticle size with a value, which value is in the range of 4-7 micronsto produce said ultra-fine powder having a targeted D5 minimum particlesize with a selected value in the range 4-7 microns.
 8. The method asdefined in claim 7 wherein said targeted maximum particle size D95 ofsaid ultra-fine powder is 15 microns.
 9. The method as defined in claim8 wherein said targeted minimum particle size D5 of said ultra-finepowder is 5 microns.
 10. The method as defined in claim 7 wherein saidtargeted minimum particle size D5 of said ultra-fine powder is 5microns.
 11. The method as defined in claim 7 wherein said firstclassifier is in said mill.